1. Field of the Invention
The invention relates to voltage generation and, more particularly, to voltage generation internal to memory systems.
2. Description of the Related Art
Memory cards are commonly used to store digital data for use with various products (e.g., electronics products). Examples of memory cards are flash cards that use Flash type or EEPROM type memory cells to store data. Flash cards have a relatively small form factor and have been used to store digital data for products such as cameras, hand-held computers, set-top boxes, hand-held or other small audio players/recorders (e.g., MP3 devices), and medical monitors. A major supplier of flash cards is SanDisk Corporation of Fremont, Calif.
FIG. 1 is a schematic diagram of a conventional voltage generation circuit 100. The conventional voltage generation circuit 100 can provide one or more generated voltages to a memory system that provides non-volatile data storage and represents, for example, a memory card (e.g., flash card). The voltage generation circuit 100 includes a charge pump circuit 102. The charge pump circuit 102 operates to boost a lower input voltage (Vin) to produce a higher output voltage (Vout). The output voltage (Vout) is coupled to a decoupling capacitor (Cd) 104. The output voltage is also coupled to a resistor divider 106. The resistor divider 106 divides the output voltage using resistors R1 and R2. A comparator 108 couples to the resistor divider 106 and to a reference voltage (Vref). The output of the comparator 108 is fed back to the charge pump circuit 102 so that the charge pump circuit 102 can regulate the output voltage such that it remains at a substantially constant voltage level.
An output voltage, such as generated by the voltage generation circuit 100, can be supplied to a memory array that provides data storage. Typically, the voltage generation circuitry and the memory array are part of a memory system (or memory device). The memory array includes a plurality of memory elements. The memory elements are, for example, non-volatile memory elements. One of various implementations for a non-volatile memory element is a diode or antifuse type memory element. The various memory elements within the memory array can be accessed by way of bitlines and wordlines. When programming a memory element, a voltage is applied across the memory element to invoke a physical characteristic change in the memory element. As an example, when the memory element corresponds to a diode or antifuse type device, the programming of the memory element is referred to as “popping” or “blowing” the diode or antifuse. Unfortunately, however, such memory elements present current leakage paths that are temperature sensitive. Conventionally, voltage generation circuits (namely, charge pump circuits) are designed to accommodate near worst-case temperature scenarios. As a result, voltage generation circuits tend to produce significant voltage ripple or voltage overshoot across an operating temperature range. The undesired voltage ripple degrades data sensing margins with respect to reading or writing data to memory elements. The voltage ripple or voltage overshoots are particularly problematic at lower temperature ranges where loading tends to be lower. Accordingly, there is a need for improved voltage generation for memory systems.